The invention also relates to a device comprising an X-ray source, a recording device and a synchronization device suitable for carrying out the X-ray exposure synchronization method. An X-ray exposure synchronization method and a device of this kind are known from the leaflet "Philips Medical Systems", 4522 984 09241/744, DVI-V, January 1985.
During the formation of an X-ray image of an object in, for example a human body, for example a heart or blood vessel, the X-ray beam is attenuated by the object and its environment. In a human body the object to be imaged and its environment consist mainly of water, so that the X-ray beam is attenuated to substantially the same extent by the object and its environment. This results in a low-contrast image of the object. By filling the object to be imaged with a contrast agent having a comparatively high X-ray absorption, such as iodide, and by subtracting an image of the object filled with contrast agent from an image of the object recorded without contrast agent, i.e. a so-called mask image, contrast enhancement is achieved If the image of the object filled with contrast agent has been shifted with respect to the mask image due to movement of the object, artefacts will occur in the contrast-enhanced image. Notably during the formation of a series of successive X-ray images which are summed for noise integration prior to display on a television monitor, or which follow a flow of contrast agent through the object to be imaged, contrast enhancement by subtraction from a mask image will be strongly degraded by movement of the object. For the imaging of vessels situated in the vicinity of a heart, the problems will occur due to cardiac movement. By measuring a movement rhythm of an object by means of the recording device, for example the formation of an electrocardiogram, exposure can be synchronized with the movement rhythm. This takes place, for example in the Philips DVI-V system. Because the exposure is performed after a predetermined delay with respect to a recording pulse supplied by the recording device, the X-ray images are in phase and register with the mask image. This has a drawback in that in the event of fluctuations of the movement rhythm of the object to be imaged, caused, for example by the contrast agent, the X-ray images will show the object in different positions, so that artefacts will occur still when this X-ray exposure synchronisation method is used.